The present invention relates to chip resistors. More particularly, the present invention relates to chip resistors designed to tolerate high surge current.
In a number of applications, chip resistors are required to dissipate pulsed electrical power. Such applications include protective circuitry for communication lines, motor drives, and power supplies. In these and other applications, voltages are applied to the terminals of the resistor for short time periods. Sometimes this is referred to as pulse loading. This amount of time of each pulse is commonly less than one second.
The general problem with using chip resistors in applications and environments which involve pulse loading relates to the magnitude of the instantaneous pulsed power. The instantaneous pulsed power may be many times higher than the steady state power rating of the resistor. When the instantaneous power is great enough or applied for a long enough time period, the result is resistor failure. Thus the problem is to maximize the pulsed power that may be safely dissipated by the resistor.
Various prior attempts at solving this problem have been made. One such attempt applicable to thick film resistor chips involves laser trimming. One example of laser trimming a thick film resistor chip is found in U.S. Pat. No. 5,874,887 to Kosinski. In the laser trimming of Kosinski, special methods are used to smooth the electrical current distribution in the resistive film through specially oriented or positioned cuts. Another prior art attempt has involved giving up on the use of laser cutting. One example of such a device is the SG73 Flat Chip Surge Current Thick Film resistor available from KOA.
Another approach has involved using special types of resistor pastes. Special resistor pastes are used to form restive film that is more tolerant to pulse loading as compared to the resistive film originating from a regular resistive paste. One example of the use of resistor pastes is disclosed in U.S. Pat. No. 5,464,564 to Brown.
Despite these attempts, problems remain. Therefore, it is a primary object of the invention to improve upon the state of the art.
It is a further object of the present invention to provide a chip resistor that has improved tolerance for instantaneous pulsed power.
Another object of the present invention is to provide a chip resistor that has improved tolerance for instantaneous pulsed power without increasing the size of the chip.
Yet another object of the present invention is to provide a chip resistor that is not susceptible to solder joint fatigue caused by multiple pulse applications.
A further object of the present invention is to provide a chip resistor that is not limited to a particular manufacturing process and can be a thick-film resistor, thin-film resistor, or a foil resistor.
A still further object of the present invention is to provide a chip resistor that can be efficiently manufactured without substantially increasing manufacturing costs.